Although many animals have vocal cords just alike as man, they cant speak. this is beacuse of they didn't have any language to talk. and their vocal cords doesn't support them and let them to talk due to their immobility of brain. 
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your not welcome
i saw u as my elder sis and u ..just ignored me,,,,
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Every animal has its own language or rather a particular sound through which it communicates.We say only humans speak because only our language can be identified and understood by us.Just as we can't speak like  a dog,cat or pigeon ; similarly they can't speak our language or in other words talk. There is no such thing like only humans can talk.The only difference is that humans only understand their ways of communication and animals understand theirs.

Hope i helped u :)